It really depends on who you build with and what they have on offer. Some builders offer a complete package with things like flooring, curtains, landscaping etc all done, but it limits your choices. Our current builder doesn't even include storm water drainage in our costs.

I've heard as a rule of thumb it is good to give yourself an extra 30% to do a nice job of extras.

The homeone website is fantastic for asking questions like this. Huge user base building all around Australia with almost any builder that you care to ask about, and much better ideas on costs to get things done